Biology subjects

Rooke, S.

Publications and source records attributed to Rooke, S..

4 recordsLinked to original sources

bioRxiv2025

Patterns of Ocular Dominance are in the Eye of the Beholder

Ocular Dominance Columns (ODCs), structures in the early visual cortex that demarcate inputs from each eye, have been observed in a wide range of mammals. The extent and arrangement of these columnar structures can vary drastically from species to species, and even along the visual cortex of a single individual. While previous studies show that these structures can form by competitive Hebbian learning, the relationship between system parameters and the resulting organizational patterns remains unclear. Here, we use a mesoscopic model of V1 development to explain how the different observed patterns of ocular dominance (columns, islands, and monocular) can arise through local Hebbian competition, as a function of the density of projections from each eye and cortical interaction strengths. We argue that our results explain the broad cortical organizational differences between species which have forward-facing versus steeply angled eyes. We additionally show that spatially varying retinal input projections, which can arise from a combination of retinotopy and varying cell density, can lead to coexistence of multiple ocular dominance patterns along the cortical sheet, consistent with experimental observations.

biophysics↗

bioRxiv2024

Trading Place for Space: Increasing Location Resolution Reduces Contextual Capacity in Hippocampal Codes

Many animals learn cognitive maps of their environment - a simultaneous representation of context, experience, and position. Place cells in the hippocampus, named for their explicit encoding of position, are believed to be a neural substrate of these maps, with place cell "remapping" explaining how this system can represent different contexts. Briefly, place cells alter their firing properties, or "remap", in response to changes in experiential or sensory cues. Substantial sensory changes, produced, e.g., by moving between environments, cause large subpopulations of place cells to change their tuning entirely. While many studies have looked at the physiological basis of remapping, we lack explicit calculations of how the contextual capacity of the place cell system changes as a function of place field firing properties. Here, we propose a geometric approach to understanding population level activity of place cells. Using known firing field statistics, we investigate how changes to place cell firing properties affect the distances between representations of different environments within firing rate space. Using this approach, we find that the number of contexts storable by the hippocampus grows exponentially with the number of place cells, and calculate this exponent for environments of different sizes. We identify a fundamental trade-off between high resolution encoding of position and the number of storable contexts. This trade-off is tuned by place cell width, which might explain the change in firing field scale along the dorsal-ventral axis of the hippocampus. We demonstrate that clustering of place cells near likely points of confusion, such as boundaries, increases the contextual capacity of the place system within our framework and conclude by discussing how our geometric approach could be extended to include other cell types and abstract spaces.

neuroscience↗

bioRxiv2024

Time Makes Space: Emergence of Place Fields in Networks Encoding Temporally Continuous Sensory Experiences

The vertebrate hippocampus is believed to use recurrent connectivity in area CA3 to support episodic memory recall from partial cues. This brain area also contains place cells, whose location-selective firing fields implement maps supporting spatial memory. Here we show that place cells emerge in networks trained to remember temporally continuous sensory episodes. We model CA3 as a recurrent autoencoder that recalls and reconstructs sensory experiences from noisy and partially occluded observations by agents traversing simulated arenas. The agents move in realistic trajectories modeled from rodents and environments are modeled as continuously varying, high-dimensional, sensory experience maps (spatially smoothed Gaussian random fields). Training our autoencoder to accurately pattern-complete and reconstruct sensory experiences with a constraint on total activity causes spatially localized firing fields, i.e., place cells, to emerge in the encoding layer. The emergent place fields reproduce key aspects of hippocampal phenomenology: a) remapping (maintenance of and reversion to distinct learned maps in different environments), implemented via repositioning of experience manifolds in the networks hidden layer, b) orthogonality of spatial representations in different arenas, c) robust place field emergence in differently shaped rooms, with single units showing multiple place fields in large or complex spaces, and d) slow representational drift of place fields. We argue that these results arise because continuous traversal of space makes sensory experience temporally continuous. We make testable predictions: a) rapidly changing sensory context will disrupt place fields, b) place fields will form even if recurrent connections are blocked, but reversion to previously learned representations upon remapping will be abolished, c) the dimension of temporally smooth experience sets the dimensionality of place fields, including during virtual navigation of abstract spaces. Code for our experiments is available at1.

neuroscience↗

bioRxiv2019

The genome of Caenorhabditis bovis

The free-living nematode Caenorhabditis elegans is a key laboratory model for metazoan biology. C. elegans is also used as a model for parasitic nematodes despite being only distantly related to most parasitic species. All [~]65 Caenorhabditis species currently in culture are free-living with most having been isolated from decaying plant or fungal matter. Caenorhabditis bovis is a particularly unusual species, having been isolated several times from the inflamed ears of Zebu cattle in Eastern Africa where it is believed to be the cause of bovine parasitic otitis. C. bovis is therefore of particular interest to researchers interested in the evolution of nematode parasitism and in Caenorhabditis diversity. However, as C. bovis is not in laboratory culture, it remains little studied and details of its prevalence, role in bovine parasitic otitis and relationships to other Caenorhabditis species are scarce. Here, by sampling livestock markets and slaughterhouses in Western Kenya, we successfully reisolate C. bovis from the ear of adult female Zebu. We sequence the genome of C. bovis using the Oxford Nanopore MinION platform in a nearby field laboratory and use the data to generate a chromosome-scale draft genome sequence. We exploit this draft genome to reconstruct the phylogenetic relationships of C. bovis to other Caenorhabditis species and reveal the changes in genome size and content that have occurred during its evolution. We also identify expansions in several gene families that have been implicated in parasitism in other nematode species, including those associated with resistance to antihelminthic drugs. The high-quality draft genome and our analyses thereof represent a significant advancement in our understanding of this unusual Caenorhabditis species.

genomics↗